I would add all of them to your 150g. Sounds like you have plenty of filtration to handle more bichirs, even lower jaw ones that can get huge like endlies. 9 bichirs in a 5x2x2 doesn't sound like too many to me. If you look at FishNCash's old threads, he had 50+ bichirs in his 150g tank with the same footprint and they did fine. You could probably add many more to your tank as long as the filtration was enough and you kept up with water changes.
6'x2.5'x2.5' = ~280 US gallons. That's enough space to divide the tank into a 2'x2.5'x2.5' section and a 4'x2.5'x2.5' section. Smaller space for the ropes and anything else that might get eaten by your Ornate and future Endlis and Laps.
Or you can keep your 70 up and running too, so you can more easily separate them by size.